Can Character X defeat or fight Character Y?

This question is very speculative and the reason is was directed here is because this fight or clash has never occurred and thus the creator, Tite Kubo, has not definitively decided the winner of this match.

If the two characters are drastically outmatched like a Lieutenant facing a Captain then it can be safe to assume the lower-ranked character would be at a disadvantage.

The same can be said for an Espada fighting a normal Arrancar without a rank.

However, this is all speculation as that fight did not occur and we do not have a factual answer for it.